In applicant's co-pending Published International Application WO92/22938, there is disclosed a dual polarization waveguide probe system in which a waveguide is incorporated into a low-noise block receiver in which two probes are located for receiving linearly polarized energy of both orthogonal senses. The probes are located in the same longitudinal plane on opposite sides of a single cylindrical bar reflector which reflects one sense of polarization and passes the orthogonal signal with minimal insertion loss and then reflects the rotated orthogonal signal. The probes are spaced λg/4 from the reflector where λg is the wavelength of the signal propagating in the waveguide. A reflection rotator is also formed at one end of the waveguide using a thin plate which is oriented at 45° to the incident linear polarization with a short circuit spaced approximately a quarter of a wavelength (λg/4) behind the leading edge of the plate. This plate splits the incident energy into two equal components in orthogonal planes, one component being reflected by the leading edge and the other component being reflected by the waveguide short circuit. The resultant 180° phase shift between the reflected components causes a 90° rotation in the plane of linear polarization upon recombination so that the waveguide output signals are located in the same longitudinal plane.
Furthermore, in applicant's co-pending International Patent Application PCT/GB96/00332, an improved dual polarization waveguide probe system was disclosed for use with a wider frequency range transmitted by new satellite systems. In this improved probe, a reflective twist plate was provided within the probe housing, the reflective twist plate having at least two signal reflecting edges so that at least two separate signal reflections are created. The multiple signal reflections enable the probe system to operate over a wider frequency range with minimal deterioration and signal output.
Although the improved version provides a better frequency response across the frequency range, it has been found that the amount of loss at the edges of the band still cause a significant performance degradation. With the increasing number of channels being used in satellite systems, it is desirable to be able to operate across the entire frequency band with substantially the same performance, to provide minimal degradation at the edges of the frequency band.